A segment of autologous saphenous vein will be anastomosed end to side between the external iliac arteries in dogs and horses. The animals will be divided in 3 groups according to the angle of the graft to the proximal artery. The protocol included acute experiments in dogs and horses and chronic experiments in dogs with a survival period of six months. Using a hot film anemometer, the velocity of flow will be measured at different sites of the vein grafts both at the time of surgery and six months later. The volume flow, the arterial pressure and the tension of the vein wall will be also recorded and correlated with the angulation of the graft. In a selected number of experiments, the uptake of albumin by the vein wall will be measured in acute experiments as well as in chronic experiments with a survival of six months. The hemodynamic data will be correlated with the histological changes. The role of wall shear stress in the development of intimal proliferation in autologous arterio-venous grafts will be examined.